Heretofore, diaphragm type pressure detectors utilizing pressure detecting elements (for example, pressure sensitive elements) have been widely used for detecting hydrostatic pressures in conduit lines (for example, refer to patent document 1).
FIGS. 9 to 11 show examples of a conventional diaphragm type pressure detector 30. The pressure detector 30 is composed of a sensor base 31, a pressure detecting element 32, a diaphragm base 34 including a diaphragm 33, a pressure transmission medium 35 (silicone oil), a sealing ball 36, a lead pin 37, and other components. When a hydrostatic pressure 38 applied onto the pressure detecting element 32 via the diaphragm 33 and the pressure transmission medium 35, a voltage signal which is proportionate to the pressure from a semiconductor pressure transducer forming the pressure detecting element 32 is output to the outside via the lead pin 37.
FIGS. 12 to 14 are enlarged fragmentary cross-sectional views which show examples of the structure for attaching the diaphragm type pressure detector 30 mentioned above to the conduit lines and the like, where the pressure detector 30 is attached and fixed into a insertion hole 40 of an attachment tool main body 39 attached to the pipelines or mechanical devices by a pressing member 41 and a fastener 42 through a gasket 43 in an airtight manner.
That is, the pressure detector 30 is attached to the inside of the insertion hole 40 of the attachment tool main body 39 through the gasket 43 in an airtight manner by sequentially inserting the gasket 43, the pressure detector 30 and the pressing member 41 into the insertion hole 40 of the attachment tool main body 39, tightening and fixing the pressing member 41 by the fastener 42 and bolts (not illustrated) to the attachment tool main body 39 side, and pressing a flange portion 34a of the diaphragm base 34 or both flange portions 31a, 34a of a sensor base 31 and the diaphragm base 34 by the front end of the pressing member 41.
In the structure for attaching the pressure detector 30, when the pressing member 41 is tightened and fixed to the attachment tool main body 39 side by the fastener 42 and bolts, compressive forces in the upward and downward directions (reactions in the upward and downward directions) are applied onto the flange portion 34a of the diaphragm base 34 or both flange portions 31a, 34a of the sensor base 31 and diaphragm base 34 through the pressing member 41 and the gasket 43.
During tightening and fixing by the pressing member 41, if a stress should be applied on the diaphragm 33 because of the compressive forces applied to the flange portion 34a of the diaphragm base 34 or both flange portions 31a, 34a of the sensor base 31 and the diaphragm base 34 in the upward and downward directions (for example, even when components of the compressive forces in the upward and downward directions are generated, and these are applied onto the diaphragm 33), a shallow groove 34b provided on the flange portion 34a of the diaphragm base 34 and a shallow groove 31b provided on the flange portion 31a of the sensor base 31 make the wall thickness of this portion small, and therefore the displacement due to the stress is absorbed in the vicinity of the thin portion.
This prevents the stress from being directly transmitted to the diaphragm 33, and prevents the diaphragm 33 from being deformed.
Consequently, in the structure for attaching the conventional pressure detector 30, changes in output and temperature characteristics before and after the pressure detector 30 is attached to the attachment tool main body 39 become extremely small, and excellent practical effects are produced.
However, in the structure for attaching the conventional pressure detector 30 mentioned above, when the pressure detector 30 is fixed to the insertion hole 40 of the attachment tool main body 39, it is difficult to completely eliminate the stress warping of the diaphragm 33, and there is the problem that the output and temperature characteristics change before and after the integration of the pressure detector 30 to the attachment tool main body 39.
This is because the extremely thin diaphragm 33 having a thickness of about 0.05 mm to 0.06 mm is provided in a position near the flange portion 34a of the diaphragm base 34 on which the compressive forces in the upward and downward directions are applied, and therefore a component of the compressive force is inevitably applied on the diaphragm 33.
Moreover, the fastener 42 and bolts may be loosened after the integration of the pressure detector 30 into the attachment tool main body 39 due to aged deterioration and the pressing force of the pressing member 41 may be lowered in some cases. In this case, there is the problem that the compressive force applied to the flange portion 34a of the diaphragm base 34 or both flange portions 31a, 34a of the sensor base 31 and the diaphragm base 34 is changed and the stress applied on the diaphragm 33 is also changed, so that the output and temperature characteristics are greatly varied.